Bird Ecology and Conservation A Handbook of Techniques

28 |Bird census and survey techniques

(a)

(b)

(d)

(c)

Most birds

Fewest birds

Fig. 2.5Choosing the right sampling units to count from a grid. (a) First, break
the whole area down into bits that can be counted—these are sampling units. In
this example, we have the resources to count 5 of the 25 sampling units. (b) Next
select your squares randomly (see text), count the birds (filled symbols) in these
specially selected sampling units (and no others), and estimate the population.
The estimate
number of birds counted divided by number of squares counted
(
average density of birds per square) multiplied by the total number of squares.
Thus, for example, population estimate
6/5 25
30. Or, more correctly,
add your census count to an estimate of the number of birds in the remaining
un-surveyed squares
6 (6/520)
30. This extrapolatesdata from areas